Antennas for use in satellite television reception only (TVRO) systems, are well known in the art. These dish-type antennas are used by a homeowner to receive satellite broadcast television programs from any one of a number of satellites in geosynchronous orbit over the equator. Each antenna includes as major components the dish or reflector which is oriented towards the satellite, and a feed which is located at the focal point of the dish. The dish or reflector ranges in size from approximately a four-foot diameter to an eleven-foot diameter and the antennas are generally mounted for rotational movement atop a pole which is anchored in a concrete pad or the like.
One of the reasons for the size of these main reflector dishes is that it is an important factor in determining the quality of the reception. The cross-sectional area of the main reflector dish projected into a plane defines the aperture of the dish, and the larger the aperture, the better the reception, all other things being equal. Therefore, a larger dish size adds to performance, but it creates problems focusing the dish on individual satellites, keeping the dish focused on the desired satellite, and also moving it from satellite to satellite at the operator's command. As the wind picks up velocity, the antenna has a tendency to shift, drift or oscillate, a phenomenon known as mispointing, such that the television reception is degraded. Therefore, it is important to be able to accurately, reliably, and rigidly point and move the dish in spite of the wind.
In the prior art, devices known as antenna actuators are commonly used to position and move the antenna along its azimuth. The antenna actuators generally comprise a longitudinal drive cylinder which is clamped to the pivotal mount with its piston bolted to the rear of the dish. An electric motor is typically used to drive the piston in and out of the cylinder, the piston generally taking the form of a spiral gear, much like a hydraulic jack, to move the antenna dish from side-to-side, and thereby adjust the azimuth. These antenna actuators are generally installed in the field after the elevation and declination of the antenna has been determined and the main reflector dish oriented at the proper angle. As is well known in the art, each installation must separately be adjusted for an initial elevation which is the angle of the pivotal rotation of the dish with respect to horizontal, and the declination of the dish which is the relative angle of the dish with respect to the pivotal rotational axis. After these have been determined, the actuator may then be mounted to provide movement along the azimuth, or in the horizontal direction. Once the actuator is installed, the declination may not be adjusted except by disassembling or removing the actuator.
To solve these and other problems in the prior art, the inventors herein have succeeded in designing an antenna with an integral azimuth track and drive which provides great accuracy and rigidity, and while at the same time permits the declination and elevation of the main reflector dish to be made without disconnection or disassembly of the azimuth drive. This improved integral azimuth drive comprises a generally circular azimuth track which is bolted to the superstructure supporting the main reflector dish, and a trolley drive means which contains a worm gear and motor and which slides over the track. The pivotal mount for the main reflector dish provides a convenient structure to secure the trolley member, so that as the drive motor drives the worm gear, the worm gear drives the track, and the track moves with respect to the pivotal mount instead of vice versa. The trolley member has an enclosure which has integrally formed ears extending along a U-connector, the U-connector being a part of the pivotal mount for the antenna dish. Thus, as the declination of the dish is changed with respect to the pivotal mount, the trolley member ears and enclosure merely slide vertically along the back of the U-connector as the vertical position of the trolley member with respect to the U-connector is irrelevant. It is only necessary that the trolley member be engaged by the U-connector so that as the drive motor turns the worm, the track is moved horizontally instead of the trolley member moving along the track.
Because of the nature of the design, the various portions of the antenna utilized in the azimuth track and drive can be made from injection molded plastic. This includes the main dish supporting superstructure, various portions of the pivotal mount including the U-connector, and the azimuth track and worm gear.
The principal advantages and features of the invention have been described. However, a greater understanding and appreciation for the invention may be obtained by referring to the drawings and detailed description of the preferred embodiment which follows.